The libsignal extension module provides cryptographic functions for
Hydra/DGD, required for
signal-server.
Building requires OpenSSL 1.1.1 or later and a side-by-side git checkout of the
standard DGD extension modules. Build
those first, and then build the libsignal module with make in
libsignal/src. The libsignal module will be placed in the lpc-ext top
directory.